Isomerization process



March 8, 1966 J. T. CABBAGE ISOMERIZATION PROCESS Filed Sept. 14, 1962 3,239,573 ISOMERIZATION PRUCESS John T. Cabbage, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Filed Sept. 14, 1962, Ser. No. 223,761 6 Claims. (Cl. 260--666) This invention relates to an improved process for the isomerization of C6 hydrocarbons. In one of its aspects, this invention relates to an improved process and appart.- tus for the production of high purity cyclohexane. In another one of its aspects, this invention relates to a process and apparatus for the isomerization of cyclohexane to methylcyclopentane.

In a conventional isomerization process for the production of high purity cyclohexane from a C6 hydrocarbon feed, isohexane is separated by fractionation from the C6 hydrocarbon feed. The substantially isohexane-free hydrocarbon mixture is further fractionated to produce a normal hexane-methylcyclopentane fraction (containing limited quantities of higher boiling materials) for isomerization to isohexane and cyclohexane, respectively. High purity cyclohexane is then easily fractionated from the isomerized material because of the limited quantities of heavy materials in the feed and the large spread in boiling points between methylcyclopentane and cyclohexane. Naturally occurring cyclohexane may be present in the raw C6 hydrocarbon feed in concentrations near 6 L.V. percent. Most of this material must be rejected from the isomerization 4feed in order to remove the intermediate boiling 2,2- and 2,4-dimethylpentane irnpurities. This substantially reduces the ultimate recovery of high purity cyclohexane from the raw feed.

Accordingly, an object of my invention is to provide an isomerization process and apparatus for the maximum recovery of cyclohexane from a C6 hydrocarbon feed.

Another object of my invention is to provide a process for the recovery of cyclohexane from a hydrocarbon feed containing said cyclohexane and 2,2- and 2,4-dimethylpentane.

Another object of my invention is to provide a process and apparatus for the isomerization of cyclohexane.

Another object of my invention is to provide a process and apparatus for the production of high purity methylcyclopentane.

Other objects, advantages and features of my invention will be readily apparent from the following description and the appended claims.

By my invention I provide an isomerization process for the maximum recovery of cyclohexane from a C6 hydrocarbon feed mixture comprising the steps of (l) separating an isohexane fraction from said C6 hydrocarbon feed mixture, (2) -fractionating the remainder of said C6 hydrocarbon mixture into a methylcyclopentane fraction and a residual hydrocarbon fraction, (3) passing said residual hydrocarbon fraction to an isomerization process step whereby the cyclohexane contained therein is isomerized to methylcyclopentane, (4) combining said methylcyclopentane fraction and the methylcyclopentane produced from the isomerization step, and (5) isomerizing the combined methylcyclopentane fractions to cyclohexane.

The drawing is a schematic representation of one embodiment of the inventive process.

3,239,573 Patented Mar. 8, 1966 A better understanding of the inventive process can be obtained by referring to the drawing. A C6 hydrocarbon feed normally comprising n-hexane, isohexane, methylcyclopentane, benzene, cyclohexane, isoheptanes and minor proportions of isobutane, normal butane, isopentane and heavy residual hydrocarbons is passed via conduit means 10 to a distillation column 11. Within distillation column 11, isohexane and lighter hydrocarbons are separated from the hydrocarbon feed mixture and withdrawn from distillation column 11 via conduit means 12. Typical operating conditions within distillation column 11 are a temperature in the range of 220 F. to 257 F. and a pressure in the range of 55 p.s.i.a. to 63 p.s.i.a., respectively. A substantially isohexane-free hydrocarbon stream is withdrawn from distillation column 11 via conduit means 13 and passed to a demethylcyclopentanizer column 14.

Within demethylcyclopentanizer column 14 a methylcyclopentane fraction is separated from the hydrocarbon feed mixture and withdrawn from column 14 via conduit means 16. A hydrocarbon residual fraction containing isoheptanes, 2,2- and 2,4-dimethylpentane and cyclohexane is withdrawn from column 14 via conduit means 17. Operating temperatures and pressures within column 14 are maintained typically within the range of 249 F. to 289 F. and in the range of 55 p.s.i.a. to 64 p.s.i.a., respectively.

Benzene contained in the methylcyclopentane fraction withdrawn from column 14 via conduit means 16 is hydrogenated to cyclohexane by passing the methylcyclopentane fraction to a conventional benzene hydrogenation zone 18. Within benzene hydrogenation zone 18 the methylcyclopentaue fraction is contacted with hydrogen in the presence of a hydrogenation catalyst such as nickel at a temperature in the range of 350 F. to 500 F. A benzene-free hydrocarbon eliiuent is Withdrawn from benzene hydrogenation zone 18 via conduit means 19.

The hydrocarbon efliuent from benzene hydrogenation zone 18 is passed Via conduit means 19 to a liquid isomerization zone 26 wherein the methylcyclopentane within the hydrocarbon feed mixture is isomerized to cyclohexane by contacting the hydrocarbon feed with a conventional isomerization catalyst such as an HC1 promoted aluminum halide complex-type catalyst. When employing an aluminum halide complex-type catalyst, the temperature and pressure of the isomerization zone is preferably maintained typically in the range of F. to F. and in the range of 100 p.s.i.a. to 250 p.s.i.a., respectively. The isomerization zone eluent is separated from the catalyst and promoter by conventional means and withdrawn from isomerization zone 20 via conduit means 21.

The isomerization zone effluent withdrawn from isomerization zone 20 via conduit means 21 is passed to a demethylcyclopentanizer column 22 wherein methylcyclopentane and lighter hydrocarbons are separated from the hydrocarbon feed mixture and withdrawn from column 22 via conduit means 23. It is within the scope of this invention to condense and recycle the methylcyclopentane and lighter hydrocarbon fraction withdrawn from column 22 via conduit `means 23 to distillation column 11, thereby recovering the methylcyclopentane not isomerized in isomerization zone 20 and recycling the recovered methylcyclopentane to isomerization zone 2G. A hydrocarbon 3 mixture comprising cyclohexane and heavier hydrocarbons is withdrawn from column 22 via conduit means 24. The temperature and pressure of column 22 -is maintained typically in the range of 237 F. to 285 F. and inthe range of 55 p.s.i.a. to 63 p.s.i.a. respectively.

The hydrocarbon mixture withdrawn from column 22 via conduit means 24 is passed to a conventional distillat-ion column 26 wherein cyclohexane is separated from the hydrocarbon feed mixture and withdrawn from distillation column 26 via conduit means 27. A residual hydrocarbon fraction is withdrawn from distillation col- `umn 26 via conduit means 28 and removed from the isomerization process. Distillation column 25 is operated at a temperature in the range of, for example, 250 F. to 260 F. and a pressure in the range of 45 p.s.i.a. to 50 p.s.1.a.

It is considered to be within the skill of the art to provide means for heating and reuxing columns 11, 22 and 26 and to provide conventional means of uid transmission and process control not herein illustrated. It is also considered -to be within the skill of the art to provide means for heating and cooling process streams. Such `lheating and cooling means except where herein illustrated are considered to be conventional and within the skill of the art.

The isomerization of the cyclohexane contained in the vresidual hydrocarbon fraction withdrawn from column 14 to methylcyclopentane will hereinafter be discussed as applied to the isomerization of cyclohexane in the presence of a platinum-type catalyst, such as Penex catalyst described in U.S. Patent 2,900,425, August 18, 1959. Other Visomerizat-ion catalysts usually comprising alumina containing minor amounts of a metal of the platinum group, such as ruthenium, rhodium, palladium, osmium, iridium `and platinum, promoted by `a minor amount of combined halogen can, of course, be employed. The residu-al hydrocarbon fraction is combined with hydrogen passed to conduit means 17 via conduit means 28 and the combined mixture passed to a heat exchange means, such as a furnace k27, wherein the combined mixture is heated.

The heated mixture is passed from furnace 27 via conratio of hydrogen to hydrocarbon in the feed mixture passed to reactor 30 is maintained in the range of 1:1

An effluent mixture is withdrawn from reactor 30 -via conduit means 31 and passed to a heat exchange means V32 whereby the hydrocarbon fraction in the reactor etiiuent is condensed. The temperature of the vaporous and liquid mixture withdrawn from heat exchange means 32 is maintained at about 100 F. The vaporous and liquid mixture is passed from heat exchange means 32 via conduit means 3 to a separator '34. Hydrogen is withdrawn from separator 34 via conduit means 36, compressed via compressor means 37 and passed via conduit means 28 to conduit means 17 in the heretofore described manner. Makeup H2, as required, is passed to conduit 36 via conduit means 35.

A liquid hydrocarbon mixture is withdrawn from separator 34 via conduit means 38 and passed to a stripper 39. Within stripper 39, the C5 hydrocarbon and lighter fraction is separated fromthe feed mixture and withdrawn from stripper 39 via conduit means 40. The hydrocarbon mixture comprising C6 and heavier hydrocarbons is withdrawn from stripper 39 via conduit means 41 and passed to a dehexanizer column 42. The temperature and the following example is presented.

4. pressure of stripper 39is typically maintained in the range of 270- to 340 Fi' and in the range of 135 p.s.i.a. to 140 p.s.i.a, respectively.

Within dehexanizer column v42, a C7 hydrocarbon fraction is separated from the hydrocarbon feed mixture and withdrawn from dehexanizer column 42 i via conduit means 43. A vaporous methylcyclopentane portion containing cyclohexane is withdrawn: from dehexanizer column 42 via'conduit means` 44 and condensed by .a means not herein illustrated.

Column 42 can be operated as a dehexanizer4V column, as herein illustrated, orfit can vbe operated to produce a high .purity methylcyclopentane product having a purity of at least V volume percent. When producing a high purity methylcyclopentane product, column ,42 is operated so as to produce a residual fraction containing cyclohex-y ane not isomerized inV reactor` 30, 2,2- and 2,4-dimethylpentane not converted in reactor 30, and kheavier hydrocarbons. ated to produceva cyclohexane fraction forrecycle to reactor 30 and a second residual fraction.

As in the case of columns 11, 14, 22 and 26, it is within the skillof the art to provide means; for heating and re-` uxing columns 39 and 42, not herein illustrated.

In isomerizing cyclohexane to methylcyclo'pentane at a tempera-ture in the range of 650-750 F. theforrnation of benzene-a process problem of high temperature prior art processes-in the isomerization zone has .beensub-` stantially eliminated. This enables the recovery of'a high purity methylcyclopentane product having a productpurity of at least 95 weight percent;

The methylcyclopentane can be recovered as aproduct in the illustrated Ymanner or it can be recycled Yvia con-V duit means 46 yto demethylcyclopentanizer column 14.; Although eitherl the high puri-ty methylcyclopentane .fraction or the methylcyclopentane fraction containing cyclohexane can be recycled, it is preferred for reasons of economy that the recycle methylcyclopentane stream be the productV obtained when-column 42 iis operated as a dehexanizer. p

By recycling the methylcyelopentane to column 14,.the recycle methylcyclopentane `is addedto the `methylcyclopentane in the :original-feed and the combined methyl,

cyclopentane fraction passed to isomerization zone-20 wherein the methyblcyclopentane isisomerized to cyclohexane. This recycle' process provides a method of; recovering a maximum quantity of cyclohexane from a C8 hydrocarbon yfeed mixture;

An advantage of the cyclohexanev ,to methylcyclopentaneisomerizat-ion isthat this proces converts 2,2- and- 2,4ditmethylpentane tov vZ-methyl-hex-ane, S-methylhexane and other hydrocarbons'boiling yhigher than cyclohex'ane` These materials can be removed in stre-am 43 with m-inimum methylcyclopentane-cyclohexane 1 loss from the process.

A further advantagepf recycling the methylcyclopr-.n-l tane fractionto column v14 is that a higher. purity methyl-V cyclopentane can be obtained and the conversion of cyclohexane to methylcyclopentane increased. 2,2-` and 2,'4;

present in the recycle methylcyclopentane stream is withdrawn from column 14--via conduit means -16 andthydrogenated to cyclohexane within benzenehydrogenation zone '18.-

To illustrate the effectiveness ofv the inventive process It is not intended that the invention should` be limited thereto.

This residual fraction can be further fractionwas admixed with hydrogen in the proportion of 2.5 mols hydrogen per mol hydrocanbon feed. The hydrogen and hydrocarbon mixture was contacted with I-3 Penex catalyst. The temperature of the conta-ct zone was 707 F. and the pressure within the cont-act zone was 500 p.s.i.g. A LHSV through the PeneX catalyst of 2.0 was maintained.

Hydrogen was separated from the contact zone effluent and analysis of the hydrocarbon fraction of the contact zone efuent provided the following results:

Weight percent Hydrogen 0.01 Propane 0.43 Isobutane 0.62 Normal butane 0.30 Isopentane 0.11 Neohexane 0.11 Z-methylpentane 1.48 3-methylpentane 0.89 Normal hexane 0.89 2,2- and 2,4-dimethylpentane 1.58

Methylcyclopentane 72.08

Z-methylhexane 2.28 3-methylhexane 3.37 Cyolohexane 12.48 Normal heptane and/ or DMCPs 1.88 Benzene 1.29 Residue 0.20

The cyclohexane conversion as measured by the following equation:

CyC in feed-CYCG in product CyC in feed was equal to 85.75 percent. The process efficiency as determined by the following equation:

CyC Conversion= 100 X MCP in product-MCP in feed Process eClenCy-lOOXCyCS in feed-CyC in product was equal to 95.8.2 percent. It is noted that the above highly effective process for the isomerization of cyclohexane to methylcyclopentane was cotnducted with a formation of only 1.29 weight percent of benzene. This is particularly significant when itis desired to yield a high purity methylcyclopentane product. Benzene production can be further reduced by operating at lo-wer temperatures and resulting lower conversion of cyclohexane to methylcyclopentane. The process problem of hydrogenating the benzene in the methyl-cyclopentane feed has been substantially minimized in comparison with prior art processes for the production of methylcyclopentane and cyclohexane.

As =will be evident to those skilled in the art, various modification of this invention can be made, or followed, in the light of the foregoing disclosure and discussion without departing from the spirit or the scope thereof.

l claim:

1. A process which comprises passing a hydrocarbon feed containing cyclohexane to an isomerization zone, said isomerization zone containing an isomerization cataly-st, passing hydrogen to said isomerization zone, maintaining the temperature of said isomerization zone in the range of 650-750 F., maintaining a pressure in said isomerization zone in the range of 400-500 p.s.i.g., withdrawing an effluent containing methylcyclopentane from said isomerization zone, partially condensing said effluent withdrawn from lsaid isomerization zone, passing said partially -condensed efuent to a separation zone, withdrawing hydrogen from lsaid separation zone, passing a liquid hydrocarbon mixture from said separation zone to a stripping zone, withdrawing a C5 hydrocarbon and lighter fraction from said strippin-g zone, passing a hydrocarbon mixture from said stripping zone to a distillation zone, withdrawing a methylcyclopentane product from said distillation zone, and withdrawing from said distillation zone a residual hydrocarbon fraction.

2. A -process which comprises passing a C6 hydrocarbon feed containing isohexane, methylcyclopentane, cyclohexane and isoheptanes to a first distillation zone, withdrawing an isohexane vaporous fraction from said first distillation zone, passing a liquid hydrocarbon from said first distillation zone to a second distillation zone, withdrawing from said second distillation zone a methylcyclopentane fraction, passing a residual hydrocarbon fraction from said second distillation zone to an isomerization zone, said isomerization zone containing an isomerization catalyst, passing hydrogen to s-aid isomerization zone, maintaining the temperature of said isomerization zone in the range of 1650-750" F., maintaining the pressure in said isomerization zone in the range of 400-500 psig., withdrawing an eluent containing methylcyclopentane from said isomerization zone, partially condensing said effluent withdrawn from said isomerization zone, passing said `partially condensed eiuent to a separation zone, withdrawing hydrogen from said separation zone, passing a liquid hydrocarbon from said separation zone to a stripping zone, withdrawing a C5 hydrocarbon and lighter fraction from said stripping zone, passing a hydrocarbon from said stripping zone to a third distillation zone, withdrawing methylcyclopentane from -said third distillation zone, and withdrawing from said third di-stillation zone a residual hydrocarbon fraction.

3. The process of claim 2 wherein at least a portion of lthe methylcyclopentane withdrawn from said third distillation zone is recycled to said second distillation zone.

4. A process which comprises passing a C6 hydrocarbon feed containing isohex'ane, methylcyclopentane, benzene, cyclohexane and isoheptanes to a first distillation zone, withdrawing from said first distillation zone an isohexane vaporous fraction, passing a liquid hydrocarbon from said first distillation Zone to a second distillation zone, withdrawing a methylcyclopentane fraction from -said sec-ond distillation zone, passing a liquid hydrocarbon containing cyclohexane from said second distillation zone to an isomerization zone, passing hydrogen to said isomerization zone, withdrawing an eluent containing methylcyclopentane from said isomerization zone, partially condensing said eiuent, passing said partially condensed euent to a separation zone, withdrawing hydrogen from said separ-ation zone, passing a liquid from said separation zone to a stripping zone, withdrawing a vaporous fraction comprising C5 hydrocarbon-s and lighter from said stripping zone, passing a liquid from said stripping zone to a third distillation zone, withdrawing methylcyclopentane from said third distillation zone, withdrawing a residual hydrocarbon fraction from said third distillation zone, passing at least a portion of the methylcyclopentane withdrawn from said third distillation zone to said second distillation zone, passing a methylcyclopent-ane fraction withdrawn from said second distillation zone to a benzene hydrogenation zone, withdrawing a benzene-free efuent from said benzene hydrogenation 'zone, passing said'benzene-free effluent to avsec-` ond isomerization 'zone, withdrawing an effluent containing cyclohexane from` lsaid second isomerization zone,U

passing said efuent containing cyclohexane to' a fourth distillation zone, passing a methylcyclopentane and lighter constituent fraction Withdrawn from said fourth distillation zone to said first distillation zone, passing a liquid 5. The process of claim 4 whereinthe isomerization catalyst contained within said first isomerization zone 4is va platinum-containing catalyst.

6.l The` proce-ss of clairzwh'rein the temperature and `pressure of said second distillationzoneis'maintained in theiangelof 249l to 289"r 'F. and inthe; range of 55fto 64 I p.s.i.la., respectively'.

References Cited bylthe Examinery UNITED STATES PATENTS: j 2,766,302 10/1956 Elkins 260-666 PAUL M. COUGHLAN', Primary Examiner. ALPHONSQ SULLVIYANa-Ewifvef-Q 

1. A PROCESS WHICH COMPRISES PASSING A HYDROCARBON FEED CONTAINING CYCLOHEXANE TO AN ISOMERIZATION ZONE, SAID ISOMERIZATION ZONE CONTAINING AN ISOMERIZATION CATALYST, PASSING HYDROGEN TO SAID ISOMERIZATION ZONE, MAINTAINING THE TEMPERATURE OF SAID ISOMERIZATION ZONE IN THE RANGE OF 650-750*F., MAINTAINING A PRESSURE IS SAID ISOMERIZATION ZONE IN THE RANGE OF 400-500 P.S.I.G., WITHDRAWING AN EFFLUENT CONTAINING METHYLCYCLOPENTANE FROM SAID ISOMERIZATION ZONE, PARTIALLY CONDENSING SAID EFFLUENT WITHDRAWN FROM SAID ISOMERIZATON ZONE, PASSING SAID PARTIALLY CONDENSED EFFLUENT TO A SEPARATION ZONE, WITHDRAWING HYDROGEN FROM SAID SEPARATION ZONE, PASSING A LIQUID HYDROCARBON MIXTURE FROM SAID SEPARATION ZONE TO A STRIPPING ZONE, WITHDRAWING A C5 HYDROCARBON AND LIGHTER FRACTION FROM SAID STRIPPING ZONE, PASSING A HYDRO- 